This invention relates to a so-called switching regulator which utilizes pulse width modulation to provide a stabilized output voltage and has a high power conversion efficiency as well as a high operating reliability, and more particularly it pertains to such a regulator including means for preventing a relaxation oscillator included therein from being brought into an intermittent oscillation state due to hunting phenomena tending to occur in the negative feedback control system, thereby ensuring that continuous oscillation is maintained.
Among regulated DC power supply devices are dropper-type ones and switching type ones. The dropper type power supply devices are advantageous in that the output voltage thereof can be reliably controlled by virtue of the fact that there is no element of time delay in the negative feedback control system because no smoothing circuit or the like is incorporated therein. These are disadvantageous in that high power loss occurs in the series control transistors thereof. In contrast thereto, the switching type power supply devices, which will be referred to as switching regulators, are advantageous in that the switching losses in the oscillator transistor are low. These have the disadvantage that an element or elements of time delay are inevitably introduced in the negative feedback control system due to the fact that a smoothing circuit or the like is included therein. Thus, the switching regulators are liable to be subjected to a hunting phenomena, and, as a result of which, the control of the output voltage becomes unreliable. Another problem with the switching regulators is such that departure from the region for safe operation of the oscillator transistors is liable to occur due to the fact that the oscillator transistor constitutes an inductance load.